refactor: move Value::ProcType to std::function

[27justin]

Description

As discussed in #548, this commit refactors Value::ProcType from a plain C-style function pointer Value(*)(std::vector<Value>&, VM *) into a wrapper class holding a std::function<>.

This enables lambda capture for State::loadFunction, improving flexibility.

This PR also adds two unit tests to test the relevant behaviour.

Checklist

• I have read the Contributor guide
• My code follows the style guidelines of this project
• I have commented my code, particularly in hard-to-understand areas
• I have updated the documentation if needed
• I have added tests that prove my fix/feature is working
• New and existing tests pass locally with my changes

[CLAassistant]

All committers have signed the CLA.

[coveralls]

coverage: 86.7% (-0.04%) from 86.738%
when pulling 6c142b6 on 27justin:feat/std-function
into aa74c8f on ArkScript-lang:dev.

[SuperFola]

Good job, thanks for the PR!

[SuperFola]

About the static analysis job, it fails because I badly configured it, I'll fix later no need to worry about it not passing